PITTSBURGH, September 25 (RIA Novosti) - New sanctions against Iran will be possible only after all other means of international pressure have been exhausted, Russian President Dmitry Medvedev said on Friday.

"Iran has the right to develop a nuclear program for civilian purposes but not to create nuclear weapons...Sanctions is not the best way to deal successfully with Iran, but if we run out of all other options, we could launch sanctions based on international law," Medvedev said in an address to students and professors at the University of Pennsylvania.

Iran has been under international pressure to halt uranium enrichment, used in both electricity generation and weapons production. Tehran has repeatedly rejected the demand, insisting it is pursuing a purely civilian program. Several Western powers have called for harsher sanctions against Tehran if it does not agree to halt uranium enrichment.

"I believe that together with the U.S. and other countries we must continue offering positive incentives to Iran so that the country would have a chance to conduct research in the sphere of nuclear energy, and at the same time we must pressure Tehran to make all its [nuclear] programs transparent instead of being a cause of concern for the Middle East and the whole world," the Russian president said.

"But if we fail to achieve this, we will certainly change the tone," Medvedev added.

Iran, which has already defied three sets of international sanctions, has agreed to meet with the Iran Six mediators, comprising Russia, the United States, China, Britain, France and Germany on October 1 to discuss its nuclear program.